1. Field of the Invention
The present invention relates to a multiple thermocouple sensor for use in thermal analysis. The sensor has individual thermocouples which are connected in series and are mounted on an electrically non-conductive material. The thermocouples have elements which extend at least essentially parallel to each other and are arranged in a semicircle between element junctions. The element junctions are arranged around a center to form a measuring point. Each measuring point has an electric connection. The present invention further relates to a thermal analysis oven. The oven includes an oven body which can be closed by means of a cover and can be heated by means of an electric heating device. A measuring cell including the above-described multiple thermocouple sensor is arranged in the oven.
2. Description of the Related Art
In known multiple thermocouple sensors and thermal analysis ovens of the above-described type, the individual thermocouples are mounted on a carrier material with the elements and junctions thereof by means of thin film technology, for example, by vapor depositing or sputtering in a vacuum. The thermocouples applied in this manner have a layer thickness of approximately 0.5 .mu.(1.mu. or .mu.m equalling 1/1000 mm) and 5 element junctions are provided for each measuring point (see, for example, brochures of Mettler Instrumente AG, CH-8606 Greifensee: "Modulares Thermoanalysen-System TA 2000" [Modular Thermal Analysis System], Mettler 1.7102.71.A (1973); "Mettler Thermoanalysen-System TA 3000" [Mettler Thermal Analysis System], 1986, ME-724073; "Mettler DDK Messzellen" [Mettler DSC Measuring Cells], 1988, ME-724135; "Know-How Live Mettler, Thermoanalyse" [Know-How Live Mettler, Thermal Analysis], 1988, ME-724127.
In certain cases, the thermocouple sensors composed of a thin film have low mechanical and chemical resistance which cannot be eliminated even when the thermocouples are composed of alternating element layers and insulating layers of thin film arranged between the element layers. This is because each insulating layer has the same thickness as the thermocouple element layer. The thermocouple element layer may be subject to chemical attack because of, for example, porosity of the thin films, particularly of the insulating films. Therefore, when using the known thermocouple sensor, for example, in a chemically aggressive environment, for example, in an environment containing cyanogen gas, the durability of the sensor is not ensured even if noble metals are used as element pairs. In these known multiple thermocouple sensors, the measured signal is small, for example, when the temperature difference .DELTA.T is small, so that the measurement accuracy is low. Accordingly, the sensitivity of these known sensors is in some cases not always sufficient. Moreover, as is well known, the manufacturing of thin films is expensive.
In addition, in other known multiple thermocouple sensors, the thermocouples are arranged in a star-shaped manner. However, in this arrangement, only a limited number of thermocouples can be arranged for a desired size of the measuring point (see, for example, German Auslegeschrift 1,205,598; German Offenlegungsschrift 2,233,515).
It is, therefore, the primary object of the present invention to provide a multiple thermocouple sensor of the above-described type with high sensitivity and good chemical and mechanical resistance. Also, the sensor is to be inexpensive to manufacture. Finally, the sensor is to be capable of being used in a thermal analysis oven of the above-described type.